The present invention relates to a vapor-permeable waterproof sole for shoes.
Conventional shoes with rubber soles are widely commercially available which are capable of ensuring a particular level of practicality and comfort which is appreciated most of all by young people and individuals engaged in sports; such soles, however, do not allow any transpiration of the foot.
As disclosed in Italian Patent no. 1,232,798 and in WO-A-97114326, shoes have long been known which have a rubber sole through which correct transpiration is ensured by virtue of an effective exchange of heat and water vapor between the environment inside the shoe and the outside environment. These rubber soles ensure at the same time the necessary watertightness with respect to external moisture and water.
These soles are in fact constituted by a tread made of perforated elastomer, above which a vapor-permeable and waterproof membrane is associated.
Subsequent improvements provide for the interposition of the vapor-permeable membrane between layers of protective material and/or fillers.
Shoes having such vapor-permeable soles have certainly constituted a considerable innovation with respect to what was available earlier.
On the other hand, it should be noted that practical drawbacks are observed in shoes produced with these vapor-permeable soles, due mainly to insufficient air circulation owing to the fact that the surface occupied by the perforations is much smaller than the total area of the sole.
It should also be observed that this insufficient air circulation is less than ideal also because the vapor-permeable membrane is substantially fully in contact with the rubber of the sole.
On the other hand, the number of perforations formed in the tread and their diameter must be limited in order to prevent pointed foreign objects, by entering through the perforations of the tread, from penetrating to the point of damaging or perforating the membrane.
The membrane is in fact continuously subjected to the compressive action of the foot, so that even an object which is not particularly pointed might cause damage without too much difficulty.
Reduced air circulation, on the other hand, makes it difficult to provide moisture exchange from the inside to the outside of the shoe, consequently reducing the transpiration through the membrane.
The amount of water vapor extracted from the shoe in fact increases with the rate at which the filler layer above the membrane dries, since it is the filler layer that collects the perspiration generated by the foot.
In order to increase air circulation, on the other hand, it would be necessary to increase the size of the perforated surface of the tread, with the result of a consequent increase in the vulnerability of the membrane.
It might also be possible to provide vapor-permeable rubber soles characterized by ventilation perforations in the tread which are inclined with respect to the ground resting plane.
With such a configuration of the tread, the membrane would be better protected against any punctures caused by pointed objects penetrating through the perforations.
However, in the practical production of such treads, which must be manufactured by injecting plastic material in a mold, it would be necessary to provide suitable undercuts in the mold, entailing consequent great technical difficulties and considerable structural complexities.
A further drawback affecting shoes having vapor-permeable rubber soles is noted when the tread makes contact with wet ground, since mud very easily enters the perforations to the point of accumulating on the surface of the membrane, reducing its vapor permeability.
A principal aim of the present invention is to provide a vapor-permeable and waterproof sole for shoes which allows the exchange of heat and water vapor, so as to always ensure an optimum internal microclimate as a function of the external climate, improving currently available vapor-permeable soles by solving their above mentioned drawbacks.
Another important object of the present invention is to provide a sole which effectively protects the integrity of the vapor-permeable membrane while allowing adequate air circulation.
Another very important object of the present invention is to provide a sole for shoes which is capable of keeping the inside of the shoe dry even in the presence of condensation of the water vapor produced by transpiration due to excessive external humidity.
Another object is to provide a sole in which the deposition of dirty material on the vapor-permeable membrane is prevented.
Another object of the present invention is to provide a vapor-permeable and waterproof sole whose structure can be easily adapted to the most disparate shoes, both for everyday use and for sports use.
Another object of the present invention is of provide a sole for shoes whose cost is substantially comparable to the costs of currently conventional soles.
Another object of the present invention is to provide a vapor-permeable and waterproof sole which can be manufactured with technologies and equipment which are conventional in this field.
Another object of the present invention is to provide a vapor-permeable and waterproof sole which can be used to ensure adequate air circulation even in special shoes such as safety shoes.
In accordance with one preferred aspect of the invention, there is provided a vapor-permeable and waterproof sole for shoes, comprising: a lower flat element made of shaped rubber-like material; an upper element; a membrane made of waterproof and vapor-permeable material; said lower and upper elements and said membrane being joined hermetically in the perimetric regions of mutual contact;
the sole being characterized in that said lower element has a hollow upper region delimited by a border with air passage openings formed in said border which extend radially and connect the hollow region to the outside of the shoe, and said membrane being interposed between said lower and upper elements at said hollow region.